Brent Westbrook 835e31b3ff Fix syntax error false positive on alternative match patterns (#21362) ...

Summary
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Fixes #21360 by using the union of names instead of overwriting them, as
Micha suggested originally on #21104.

This avoids overwriting the `n` name in the `Subscript` by the empty set
of names visited in the nested OR pattern before visiting the other arm
of the outer OR pattern.

Test Plan
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A new inline test case taken from the issue

2025-11-10 10:51:51 -05:00

..

err

Catch syntax errors in nested interpolations before Python 3.12 (#20949)

2025-10-20 09:03:13 -04:00

ok

Fix syntax error false positive on alternative match patterns (#21362)

2025-11-10 10:51:51 -05:00